1. Field of the Invention
The present invention relates to a rubber composition.
More precisely the present invention relates to a rubber composition which is excellent in mechanical strength and wear resistance, has a lower rolling resistance and is excellent in productivity because of its fast vulcanization velocity.
2. Background Information
Rubber compositions containing silica have been widely used for colored or white rubber because of the fact that they are more easily colored than rubber compositions containing carbon black. They have also been used for tires based on their characteristic of having a smaller loss in energy in temperatures equal to or higher than room temperature. Vulcanized rubber obtained by vulcanizing rubber compositions containing silica, however, are insufficient in mechanical strength such as tear strength, and are inferior in productivity because of their slow vulcanizing velocity.
JP-A-6-248116 discloses a rubber composition for tires containing silica in which the surface of silica was treated with an organic silica compound, for example, at 250.degree. C. for an hour. This composition, however, has the disadvantage that the vulcanized rubber obtained from the rubber composition is still insufficient in wear resistance. Furthermore, it has the disadvantage that productivity of the rubber composition is inferior because a surface-treated silica must be separately prepared by treating the surface of silica.
As a result of extensive studies with the objective of obtaining a rubber composition without these disadvantages, the present inventors have found that rubber compositions containing silica which is not surface-treated, and which are obtained by kneading under controlled temperatures of 200.degree. C. or less are excellent in wear resistance, have a lower rolling resistance and are excellent in productivity because of its fast vulcanization velocity, and thus have completed the present invention.